Field of the Invention
The present disclosure relates to a coupling structure between a sensing magnet and a plate of an EPS motor.
Discussion of the Related Art
Generally, almost every vehicle employs an electric power-assist steering system. Such an electric power-assist steering system generates an assist force based on the steering torque and the steering angle, so as to enhance the steering performance of the vehicle.
That is, a steering system that assists a steering force of a vehicle with a separate power is used to enhance the motion stability of a vehicle.
Conventionally, the auxiliary steering device uses hydraulic pressure, but an Electronic Power Steering (EPS) system adapted to transmit a rotation output of an electric motor to a steering shaft via a speed reduction mechanism has been increasingly employed these days from a viewpoint of a reduction in engine load, a reduction in weight, an enhanced steering stability and a quick restoring force.
The EPS system is such that an Electronic Control Unit (ECU) drives a motor in response to steering conditions detected by a speed sensor, a torque angle sensor and a torque sensor to enhance a steering stability and provide a quick restoring force, whereby a driver can safely steer a vehicle.
The EPS system is also such that a motor assists a torque manipulating a steering wheel to allow a driver to steer a vehicle with less power, where the motor employs a Brushless Direct Current (BLDC) motor.
The BLDC motors have been increasingly used because the brushless motors are excellent in maintenance property, have a small size, and are capable of generating a high torque. The BLDC motor generally forms an exterior look by coupling of housing and a cover member, an inner circumferential surface of the housing is provided with a stator, and the stator is centrally formed with a rotor rotatably mounted in electrical interaction with the stator. The rotor is rotatably supported by a rotation shaft, and an upper surface of the rotation shaft is connected by a steering shaft of a vehicle to provide a power assisting the steering of the vehicle as mentioned above.
The cover member is formed therein with a PCB (Printed Circuit Board) mounted with a sensing device provided in a magnetic device, where the sensing device detects a magnetic force of a sensing magnet rotatably mounted with the rotor, whereby a current position of the rotor can be checked. Generally, the sensing magnet is fixed to an upper surface of a plate mounted at an upper side of the rotor using an adhesive. In a case the sensing magnet is magnetized to the plate, the position of the rotor can be detected by coupling of the plate to the rotation shaft in response to a direction of magnetic field.
The coupling of the plate to the sensing magnet is performed using the adhesive as mentioned above. Thus, it is difficult to precisely control the adhesion process, and there is a possibility of the sensing magnet being separated. Particularly, in view of vehicular characteristics where environmental conditions vary, a coupling relation must be maintained by a coupling force of the adhesive alone, and if a motor is used under an alternating conditions of high temperature and low temperature, or exposed under a high temperature for a long time, the adhesive force of the adhesive may decrease to generate a separation of sensing magnet or a disablement of motor driving. This structure generates a difficulty in selecting a proper adhesive and an economical difficulty in selecting a high price adhesive, and poses a problem of requiring a further fine coating process of adhesive.